The present invention relates generally to presses for forming cylindrical or round bales.
These presses are of a general type which is well-known and comprise sets of flexible elements such as bands, belts or the like which, by their displacement, form, by rolling up inside a chamber provided in the body of the press, a bale of generally cylindrical or round shape from harvest products, especially forage or hay, gathered on the ground in the course of the advance of the press. When the bale has attained the desired diameter and has been bound, the rear gate of the press is opened and the bale is ejected onto the ground. The formation of another bale by rolling up can then begin inside the press.
Although, throughout the description, the term "belts" is used for greater simplicity to designate the elements which bring about the formation of the bale by rolling up within the chamber of the press, it will be understood that the invention is also concerned with machines in which other elements, such as chains, for example, are used for this purpose.
In order to ensure the formation of bales having a satisfactory density, that is to say in which the rolled up harvest products are sufficiently compacted to provide the required cohesion, avoiding all disintegration or all crumbling of the bale of forage or other material on the ejection thereof from the press onto the ground and during its subsequent handling, it is usual to subject certain of the guide rollers of the press to a biasing action which is designed to produce in the belts a tension which itself produces the compacting of the harvest products while they are being rolled up. The means which produce this biasing effect on the movable guide rollers of the press thus resist the increase in the volume of the baleforming chamber and compress the harvest products being rolled up by the tension exerted in the belts.
The density of the bales formed in a press is usually adjustable by biasing means, such as hydraulic cylinders or springs, for the guide rollers.
In the course of the operation of the press, it may happen, especially when the biasing means has been adjusted to form very dense bales and when operating the press during high humidity or when "lumps" or "packs" of harvest products are present in the windrow, that the torque delivered by the driving shaft of the press undergoes a violent increase. This violent increase in the torque then has to be compensated for by slip in the main clutch of the press. For obvious reasons, it seems to be preferable to avoid such loading of the main clutch of the press which if repeated many times results in harmful wear and tear which in turn is liable to reduce its working life.
The object of the invention is to overcome this disadvantage and to provide a press for forming cylindrical or round bales which comprise means for limiting this violent increase in the resisting torque on the driving shaft of the press resulting from an accumulation of harvest products or unfavorable working conditions.
Consequently, the invention is concerned with a press for forming cylindrical or round bales, comprising sets of bands, belts or the like which define a chamber for forming a bale by rolling up and pass over guide rollers at least one of which is driven from a main driving shaft, some of these guide rollers being movable tensioning rollers which are subjected to the action of biasing means for maintaining the belts under tension and characterized in that a resisting torque sensor is provided on the main driving shaft of the press and in that means operatively connected to this resisting torque sensor act on the biasing means of the tensioning rollers so as to adjust the biasing means in a sense that will reduce the tension of the belts when the resisting torque on the driving shaft of the press increases above a predetermined limit value.
In this case, there will usually be provided, in cooperation with one or more hydraulic tensioning cylinders forming part of the biasing means, an expansion valve in the form of an electrically operated pressure relief valve. According to a constructional form of the invention, the resisting torque sensor provided on the main driving shaft of the press generates an electrical output signal which is operatively connected to a solenoid for acting on said expansion valve so as to reduce or eliminate its response threshold when a resisting torque on the main driving shaft is sensed which exceeds a predetermined limit value. Each hydraulic tensioning cylinder acts on the movable guide rollers of the belts, usually via an arm or lever and the expansion valve is in the form of a pressure relief valve connected in shunt with the opposite ends of the tensioning cylinder. Thus, the reduction or setting at zero of the response threshold of the relief valve then produces at the same time a reduction of the working pressure of the associated hydraulic cylinder or cylinders in the same circuit and hence the tension of the belts passing over the guide rollers.
This reduction of tension enables the harvest products to be rolled up into a bale in a manner which takes into account the particular conditions which are encountered in the course of operation. As soon as the resisting torque on the main driving shaft falls once again below the predetermined limit value, the electrical output signal from the resisting torque sensor ceases to act on the expansion valve and the working pressure of the hydraulic cylinder or cylinders returns to its normal value.
According to a constructional variant, the electrical output signal of the resisting torque sensor is operatively connected to solenoid-operated shunt valve which is connected in parallel with the hydraulic tensioning cylinder or cylinders and with the expansion valve in the hydraulic circuit concerned, and this shunt valve is actuated, on the sensing of an excessive resisting torque on the main driving shaft of the press, so as to return to the reservoir the liquid delivered by the pump, causing the pressure in the cylinder or cylinders to fall and thereby effecting a reduction in tension of the belts. Here once again, as soon as the resisting torque sensed has fallen below the predetermined limit value, the shunt valve returns to its initial closed position and the pressure in the hydraulic cylinder or cylinders is thereafter regulated solely by the expansion valve.
The description which will follow, made with reference to the annexed drawings, and given non-limitatively, will enable the invention to be better understood.